[R] How to....

Jia Ying Mei jiamei at Princeton.EDU
Wed Jul 23 16:25:23 CEST 2008

Thank you very much. As for the second part, for every price change, the 
percentage of every price change can be calculated (i.e. amount of 
change divided by previous price). I was looking for a way to merely 
find the mean and median of all price change percentages for each 
country. I don't know if that's helpful or not. But thats very much for 
the first part, thats the harder part for me I think.

Jia Ying Mei

Jim Lemon wrote:
> On Tue, 2008-07-22 at 16:31 -0400, Jia Ying Mei wrote:
>> Hi everyone,
>> I am not new to R, but its been over a year since I've used it, so I 
>> don't remember how to do some things.
>> I have a data set (in excel currently, but will be converted to text), 
>> that has date, country and price, with a price for every country for 
>> every date. I need to find the mean and median of the interval between 
>> price changes for each country and the mean and median percentage change 
>> for each price change within the data for a single country.
>> How should I go about doing this? I'd appreciate any help.
> Hi Jia,
> I'm not too sure what you mean by the second set of means and medians,
> but this should get you started:
> # first make up some data
> jym.df<-data.frame(country=rep(c("au","br""cn","in","us"),each=100),
>  date=rep(as.Date("02/02/2008",
>   format="%d/%m/%Y"),500)+sample(-40:40,500,TRUE),
>  price=rnorm(500,100,20))
> # get the intervals by country - have to create a new data frame
> jymint.df<-data.frame(country=rep(levels(jym.df$country),each=99),
>  intervals=unlist(tapply(jym.df$date,jym.df$country,diff)))
> library(prettyR)
> # break down the intervals by country
> brkdn(intervals~country,jymint.df,num.desc=c("mean","median"))
> Jim

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